Plastic compositions for forming barriers against various types of radiation are known in the art. For example, U.S. Pat. No. 3,261,800 proposes a thermoplastic polymer containing from 0.05% to 70% boron nitride to provide a shield against thermal neutrons. U.S. Pat. No. 3,609,372 describes formation of a shaped body as a shield against radioactive radiation such as gamma and neutron radiation. The shield is made with a fatty acid with powdered metals that can be various different types. Other U.S. patents describing various compositions for shielding are U.S. Pat. No. 3,895,143 which proposes various powdered metals or oxides or sulfides in a latex 20 matrix to provide protection against radar, x-rays, radioactive and television radiations; and U.S. Pat. No. 4,156,147 which describes a neutron absorbing plate that uses boron carbide and silicon carbide particles.
Medical laser beams are usually characterized by focusing a large amount of radiation in a very small spot. Typically, a beam of about 20 to about 50 watts is focused to a very small area (about 0.03 mm.sup.2) so as to create a high power density (optical power per unit area) sufficient for cutting or cauterizing. The medical laser beam may be pulsed or continuous depending upon the desired mode of operation.
Medical laser beams usually have a focal point about three centimeters or less from the tip of the hand-held instrument. Beyond this focal point, the laser beam again diverges. However, the intensity of the divergent beam is still sufficient to cause eye damage and skin damage at considerable distances from the instrument. For example, the anesthesiologist is often seated behind a drape, which serves as a sterile screen. This screen, however, offers little or no protection against the laser beam. The beam is sufficiently intense to penetrate a typical paper or cloth drape and injure persons behind it. Accordingly, great care should be taken to protect the various personnel in an operating room as well as the patient against inadvertent and random oriented laser beams activations.
Various laser protection devices have been proposed. One technique frequently relied upon for the patient is a series of wet sponges surrounding the site where the surgeon needs to work. It has been found, however, that the very laser, typically a CO.sub.2 laser, used to work on a patient because its wavelength is absorbed by moist flesh, also is absorbed by the moist sponge. This absorption quickly allows the beam to form a narrow column of evaporated moisture in the sponge to then expose underlying skin to almost the full intensity of the beam. The protection of the moist sponge is, therefore, not normally sufficient against a medical laser beam.
Other U.S. patents related to laser shields employ powder in a polymer mix, U.S. Pat. No. 4,611,588; or powdered aluminum in a polymer matrix such as rubber latex, U.S. Pat. No. 4,520,814. In U.S. Pat. Nos. 4,604,998, 4,715,366 and 4,901,738, laser shields are described using metal foils such as formed of aluminum. This foil can be covered by a non-reflective surface. But when this is impacted by a medical laser beam, it tends to be quickly penetrated so that the underlying foil reflects the beam in a random, often dangerous, direction. U.S. Pat. No. 4,658,812 describes a laser shield formed of tiny glass bubbles whose sizes are in the range from 20 to 200 microns and are imbedded with or without water in a silicone matrix. Glass has a fusion temperature of the order of about 800.degree. C. and this tends to melt rather quickly when exposed to a highly powered focused laser beam.
Graphite and certain metal powders have been found to be prone to burst into flame or eject small burning particles when exposed to a high intensity medical laser beam. Burnable or readily oxidizable materials are, therefore, dangerous to a patient and personnel in an operating room. The resistance of metal foils to penetration often is inadequate when a medical laser inadvertently impacts a metal foil at full focused power for a short instance. Reflective shields, furthermore, can reflect the beam to some other spot without sufficient attenuation and consequently, only redirect the beam for damage to be caused elsewhere.
Although resistance to laser penetration is enhanced by increasing the thickness of a barrier, such improved resistance impairs the flexibility of the barrier and its ability to properly drape around a patient and personnel.